Window laser with high power reduced divergence output

Abstract

A window laser having at least one window region with a transparent waveguide layer optically coupled to an active region generating lightwaves. The waveguide layer is characterized by a broader guided transverse mode for the lightwaves than the active region and may have a thickness which is greater than the active region, a refractive index difference with respect to cladding layers which is less than a refractive index difference between the active region and the cladding layers, or both. The waveguide layer may be coupled to the active region via a transition region characterized by a gradual change in the guide mode width of the lightwaves, such as from a tapered increase in thickness of the waveguide layer in a direction away from the active region. The preferred method of making window regions having these transparent waveguides is impurity induced disordering, in which the interfaces between active region and cladding layers is smeared to produce the waveguide layer with increased bandgap and a graded transverse refractive index profile. The laser is characterized by a high power output beam with reduced far field transverse divergence.

We claim: 
     
       1. A semiconductor laser comprising, a plurality of contiguous semiconductor layers forming a semiconductor body, a portion of at least one of said layers forming an active region for lightwave generation and propagation under lasing conditions in a resonant optical cavity providing optical feedback of said lightwaves, said active region characterized by ordered semiconductor layer interfaces,   biasing means for injecting current into said active region to generate said lightwaves, and   at least one window region in said semiconductor body transparent to said light waves and having a transparent waveguide layer optically coupled to said active region, said active region being outside of said at least one window region, said transparent waveguide layer being formed from a remaining portion of the same said layers which form said active region, said transparent waveguide layer characterized by disordered interfaces, wherein said transparent waveguide layer is characterized by a single broader-guided transverse mode for said lightwaves than said active region of similar lateral extend so as to produce an output beam with a reduced transverse far field divergence.   
     
     
       2. The laser of claim 1 wherein said transparent waveguide layer has a thickness which is greater than the thickness of said active region. 
     
     
       3. The laser of claim 1 wherein said active region and said transparent waveguide layer are each bounded by semiconductor cladding layers characterized by indices of refraction which are less than the indices of refraction of said active region and of said transparent waveguide layer, the index of refraction difference between said active region and the cladding layers bounding said active region being greater than the index of refraction difference between said transparent waveguide layer and said cladding layers bounding said transparent waveguide layer. 
     
     
       4. The laser of claim 1 wherein said transparent waveguide layer is characterized by a graded transverse refractive index profile with a maximum index of refraction being located near the center of the transparent waveguide layer. 
     
     
       5. The laser of claim 1 wherein said transparent waveguide layer is optically coupled to said active region via a transition region characterized by a gradual change in the guided mode width of said lightwaves. 
     
     
       6. The laser of claim 5 wherein said the thickness of said transparent waveguide layer gradually increases in said translation region in a direction away from said active region. 
     
     
       7. The laser of claim 5 wherein said waveguide layer is characterized by thickness and bandgap values both of which being tapered in said transition region from first thickness and bandgap values in said active region to higher thickness and bandgap values in said window region. 
     
     
       8. The laser of claim 1 wherein said at least one window region with said transparent waveguide layer is characterized by a disorder inducing impurity diffused through said semiconductor layers. 
     
     
       9. The laser of claim 8 wherein a disorder inducing impurity diffused through window region is selected from the group consisting of silicon, zinc, and tin. 
     
     
       10. The laser of claim 1 wherein two window regions, each having a transparent waveguide layer, are adjacent to said pair of end facets, and said active region is centered between said two window regions. 
     
     
       11. The laser of claim 1 wherein said output beam is characterized by a continuous wave power of at least 2 Watts without causing catastrophic degradation of the pair of end facets. 
     
     
       12. The laser of claim 1 wherein said resonant optical cavity is defined between a pair of end facets, at least one of said end facets being coated with a dielectric material to a thickness of approximately one-quarter wavelength of said lightwaves in said dielectric material. 
     
     
       13. A semiconductor laser comprising, a plurality of contiguous semiconductor layers forming a semiconducor body, a portion of at least one of said layers forming an active region for lightwave generation and propagation under lasing conditions in a resonant optical cavity providing feedback for said lightwaves, said active region characterized by ordered semiconductor layer interfaces,   biasing means for injecting current into said active region to generate said lightwaves, and   at least one transparent waveguide layer in said semiconductor body and formed from a remaining portion of the same said layers which form said active region, said transparent waveguide layer characterized by disordered semiconductor layer interfaces, said transparent waveguide layer optically coupled to said active region via a transition region characterized by a gradual increase in the thickness and bandgap of said waveguide layer from first thickness and bandgap values in said active region to higher thickness and bandgap values in said transparent waveguide layer.   
     
     
       14. The laser of claim 13 wherein both said active region and said transparent waveguide layer are bounded by semiconductor cladding layers with indices of refraction less than those of said active region and transparent waveguide layer, wherein the refractive index difference between the cladding layers and said active region is greater than the refractive index between the cladding layers and said transparent waveguide layer, the refractive index difference gradually decreasing in said transition region in a direction away from said active region. 
     
     
       15. The laser of claim 13 wherein said transparent waveguide layer is characterized by a graded transverse refractive index profile with a maximum index of refraction located near the center of the waveguide layer. 
     
     
       16. The laser of claim 13 wherein said transparent waveguide layer is characterized by an impurity diffused through said semi-conductor layers. 
     
     
       17. The laser of claim 13 wherein two transparent waveguide layers are adjacent to a pair of end facets of said laser and said active region is located between said two waveguide layers. 
     
     
       18. The laser of claim 13 wherein said resonant optical cavity is defined between end facets for producing said feedback, at least one of said facets being coated with a dielectric material to a thickness of approximately one-quarter wavelength of a said lightwaves in said dielectric material. 
     
     
       19. A semiconductor laser comprising, a plurality of contiguous semiconductor layers forming a semiconductor body, a portion of at least one of said layers forming an active region for lightwave generation and propagation under lasing conditions in a resonant optical cavity, said optical cavity characterized by a first index of refraction for said lightwaves, said active region characterized by ordered semiconductor layer interfaces, said   biasing means for injecting current into active region to generate said lightwaves,   means for obtaining optical feedback of said lightwaves in said resonant optical cavity sufficient for lasing operations, and   at least one window region in said semiconductor body transparent to said lightwaves and having a transparent waveguide layer optically coupled to said active region, said active region being outside of said at least one window region, said transparent waveguide layer being formed from a remaining portion of the same said layers which form said active region, said transparent waveguide layer characterized by disordered semiconductor layer interfaces and by a second index of refraction for said lightwaves,   wherein said semiconductor layers including cladding layers bounding said active region and said transparent waveguide layer, said cladding layers characterized by indices of refraction that are less than said first and second indices of refraction, a first index of refraction difference between said transparent waveguide and said cladding layers being less than a second index of refraction difference between said active region and said cladding layers.   
     
     
       20. The laser of claim 19 wherein said transparent waveguide layer is characterized by a graded transverse refractive index profile with a maximum index of refraction being located near the center of the transparent waveguide layer. 
     
     
       21. The laser of claim 19 wherein said transparent waveguide layer is optically coupled to said active region via a transistion region characterized by a gradual change in the index of refraction difference between said transparent waveguide layer and said cladding layers. 
     
     
       22. The laser of claim 19 wherein said window regions are characterized by an impurity diffused through said semiconductor layers. 
     
     
       23. The laser of claim 19 wherein two transparent waveguide layers are adjacent to cavity defining end facets and said active region is centered between said two waveguide layers. 
     
     
       24. The laser of claim 19 wherein said optical feedback means comprising a pair of end facets defining said resonant optical cavity, at least one end facet being coated with a dielectric material to a thickness of approximately one-quarter wavelength of said lightwaves in said dielectric material.